In recent years, file server systems are known to share data with a plurality of client terminals. Such a file server system includes a storage device such as a disk device that stores therein data to be the subject of access, and an information processing apparatus such as a file server that receives an access request from a client terminal and accesses the disk device.
When such a file server receives access request from a client terminal that uses the file server system, the file server carries out an access to the disk device to obtain data from the disk device and transfers the data to the client terminal. In this process, the file server takes time, from executing the access to the disk device until retrieving the data from the disk device, such as a seek time for moving a head to a track of an access position and a rotational waiting time for the access position on a recording medium to rotate to reach the position of the head. A related art example is described in Japanese Laid-open Patent Publication No. 03-034158.
The file server system described above, however, has a tendency of access performance to deteriorate. For example, when storage areas of data of high access frequency are dispersed on the disk device, the access performance deteriorates. More specifically, when the storage areas of data of high access frequency are dispersed on a disk, the distance between pieces of the data of high access frequency becomes longer, whereby the time for the head to move and the time for the disk to rotate become longer. As a consequence, seek operation and rotational waiting operation takes longer time, whereby the access performance deteriorates.
An example of a tendency of access requests from client terminals in a file server system will be described with reference to FIG. 16. FIG. 16 is an exemplary chart for explaining the tendency of access requests from client terminals. In the example in FIG. 16, the abscissa axis represents an offset uniquely given to an area of a disk device in a unit of 1 GB, and the ordinate axis represents a rate of I/O load caused by an access to full load for each area. The example in FIG. 16 illustrate vertical lines with diamonds, squares, triangles, and Xs at their both ends representing respective load statuses. A line with diamonds represents the load status of each area caused by an access from 0:00 to 5:59 and a line with squares represents the load status of each area by an access from 6:00 to 11:59. A line with triangles represents the load status of each area caused by an access from 12:00 to 17:59 and a line with Xs represents the load status of each area by an access from 18:00 to 23:59.
As indicated in FIG. 16, accesses occur in limited areas and occur in nearly the same areas throughout the day. For example, in the example indicated in FIG. 16, no access occurs for the storage areas of offsets 1386 to 1932. Furthermore, accesses are concentrated only in limited areas making the load high, resulting in a plurality of dispersed areas with high load. For example, in the example indicated in FIG. 16, accesses are concentrated in the storage areas of offsets 378 to 420 and on the storage areas of offsets 1302 to 1344 and these storage areas of concentrated accesses are far apart from one another.
Under such a tendency, as described above, the distance between pieces of the data of high access frequency is long and the time for the head to move and the time for the disk to rotate become longer. As a result, the time it takes for the seek operation and the rotational waiting operation becomes longer, whereby the access performance deteriorates.
As a way to make a seek time and a rotational waiting time short, there is a method for causing a disk controller to move data of high access frequency to an outer circumferential zone of the disk which is faster than an inner circumferential zone of the disk. However, to realize the method of disposing data of high access frequency at the outer circumference of the disk by the disk controller, it is preferable to prepare special hardware for each disk device. The above-described issue is not limited to file servers, and it is common to information processing apparatuses that control an access to storage devices.